Coating composition for metal

Abstract

A coating composition for metallic surfaces contains: (1) Cr6+, or Cr6+ and Cr3+, (2) 1-50% of lubricant(s) dispersed by a nonionic emulsifying agent, (3) acryl-series polymer emulsion, which is obtained by emulsion-polymerizing, by means of a nonionic emulsifying agent which is essentially free of anionic and cationic emulsifying agent and which contains a polyoxyethylene-polyoxypropylene block polymer, monomers of A), B), and C): A) a monomer of ethylene-series, unsaturated carboxylic acid B) one or more monomers selected from a), b), and c): a) alkoxyethylene(metha)acrylamide and its derivative(s) expressed by the following general formula(m=0-4) b) acid phospho-oxyalkyl(metha)acrylate, and c) alkoxy-alkyl(metha)acrylate C) one or more acryl-series monomers (a part of which may consist of 2)(c)).

We claim: 
     
       1. A surface-treating composition for metallic surfaces which contains hexavalent chromium ions or hexavalent and trivalent chromium ions as an inorganic compound, and a mixture of acryl-series polymer emulsion set forth below and one or more lubricants dispersed by an emulsifying agent set forth below, wherein from 1 to 50% by weight (in terms of nonvolatile matters) of one or more lubricants as a lubricating component are dispersed by a first nonionic emulsifying agent which has been added for preventing coagulation of the lubricating component in the surface-treating composition wherein said emulsifying agent is added to the lubricating component and the emulsifying agent and the lubricating component are melted together, the surface-treating composition having a pH of 5 of less, wherein said acryl-series polymer emulsion is obtained by emulsion-polymerizing, by means of a second nonionic emulsifying agent which is essentially free of anionic emulsifying agent and cationic emulsifying agent and which contains a polyoxyethylene-polyoxypropylene block copolymer, monomers of 1), 2) and 3): 1) one or more monomer of ethylene-series, unsaturated carboxylic acid   2) one or more monomers selected from a), b), and c): a) alkoxyethylene (metha)acrylamide and its derivatives(s) expressed by the following general formula ##STR4## X is C n  H 2n+1  (n=0 or 1) Y is C m  H 2m+1  (m=0-4)   b) acid phospho-oxyalkyl(metha)acrylate, and   c) alkoxy-alkyl(metha)acrylate     3) one or more acryl-series monomers (a part of which may consist of 2) (c)) .   
     
     
       2. A coating composition for metallic surfaces according to claim 1, wherein said inorganic compound further includes at least one member selected from a group consisting of (i) phosphoric acid, (ii) silica, and (iii) one or more metal ions of cobalt, nickel, manganese, and zinc. 
     
     
       3. A coating composition for metallic surfaces according to claim 1 or 2, wherein fluoride ions are further included as the inorganic compound. 
     
     
       4. A coating composition for metallic surfaces according to claim 1, wherein the proportion of acryl-series polymer emulsion to total chromium ions is from 200 to 0.2.